Effect of conditioned media from mature human adipocytes on insulin-stimulated Akt/PKB phosphorylation in human skeletal muscle cells: role of BMI and fat cell size.
Obesity is associated with chronic low-grade inflammation. It is currently hypothesized that products secreted from fat cells not only cause this proinflammatory condition but may also have a direct impact on the development of insulin resistance in skeletal muscle. The aim of this study was to investigate if adipocyte-conditioned media interfere with insulin-stimulated Akt/PKB phosphorylation in in vitro differentiated human skeletal muscle cells. Primary human skeletal muscle cells were exposed to adipocyte-conditioned media from subjects with a wide range of BMI. Insulin-induced phosphorylation of the signaling proteins Akt/PKB and ERK-2 was analyzed using a bead-based fluorescence detection system and was correlated to BMI and fat cell size. Adipocyte-conditioned media reduced insulin-stimulated Akt/PKB phosphorylation in a manner depending on BMI and fat cell volume. This inhibition in serine phosphorylation was comparable to that observed in TNF-alpha-treated control cultures. Conditioned media from omental adipocytes reduced Akt/PKB phosphorylation moderately to a greater extent compared to media from subcutaneous fat cells from the same donors (p<0.05). Furthermore, there were significant associations between the concentration of selected adipokines and Akt/PKB phosphorylation. These data provide first direct evidence that secreted factors from freshly isolated mature fat cells separated according fat cell size reduce insulin-stimulated Akt/PKB phosphorylation in human skeletal muscle cells and may contribute to the pathogenesis of obesity-associated insulin resistance.
Skurk
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Else Kröner-Fresenius-Center for Nutritional Medicine, Life Science Center Weihenstephan, Technische Universität München, Munich, Germany. thomas.skurk@wzw.tum.de
Alberti-Huber
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Hauner
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H
D017667:Adipocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D054392:Adipokines / Q000494:pharmacology; D015992:Body Mass Index; D002454:Cell Differentiation; D002455:Cell Division; D048429:Cell Size; D003470:Culture Media; D017077:Culture Media, Conditioned / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007249:Inflammation / Q000209:etiology; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D009765:Obesity / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*
D054392:Adipokines; D003470:Culture Media; D017077:Culture Media, Conditioned; D007328:Insulin; D051057:Proto-Oncogene Proteins c-akt; D020929:Mitogen-Activated Protein Kinase Kinases